With Cambodia's rice planting season only weeks away, relief agencies are porposing an emergency airlift to Phnom Penh for shipments of rice seed long delayed by red tape. At the same time plans are being hastily laid to send huge quantities of seed across the Thai border.

Agricultural specialists estimate Cambodia needs 30,000 metric tons of seed from abroad for its main wet season rice crop this year. Only a fraction of that has been delivered to date, while shipment of the rest is being held back by Thai export restrictions.

Provision of seed has been dangerously neglected in favor of food, many people in the aid community feel. If villages have no seed at planting time, the harvest later this year will be lower than expected and Cambodia's efforts toward self-sufficiency in food in 1981 could be seriously compromised. e

For some strains of rice, farmers should begin turning the soil in mid-April, three weeks from now. Field work begins in May or June for other varieties of grain, but one relief official remarked: "No one will prepare the land if they don't see the seeds first."

UNICEF and the International Committee of the Red Cross, the two agencies coordinating the Western countries' relief effort, will shortly request permission from the Vietnamese-supported Heng Samrin government to begin air deliveries of seed in early April, assuming Thai export clearance is obtained, relief sourves said. Some 10,000 tons could be unloaded in Phonom Penh in 50 days, according to this plan.

One agency has suggested they also ask to fly seed directly to Battambang Province, the country's largest producer of rice in prewar years. Phnom Penh's thinking on these proposals is not known.

Meanwhile, momentum is growing within United Nations agencies to make a new appeal to the Heng Samrin government to open a truck or rail route from Thailand. Last fall Phnom Penh vetoed such a proposal apparently fearing that convoys would be attacked when they passed through border zones disputed by guerrillas loyal to the former Khmer Rouge government.

U.N. officers are now asking their headquarters to approach Phnom Penh at a high level on this question, aid sources said. The land link could also take the from of repairing the rail line linking the two countries. "With a railway you can move 1,000 tons at a time," remarked one official.

Some aid workers have speculated the gravity of the seed shortage might prompt Phnom Penh to drop its long-standing opposition to land transport. If it did so, Vietnamese troops would probably be deployed the secure the 30-mile corridor between the Thai frontier and the market town of Sisophon.

In the past Phnom Penh has generally insisted that supplies to villages under its control be delivered to Phnom Penh and the port of Kompong Som, then distributed by Heng Samrin government agencies. However, thee appears to be a growing sentiment among relief workers that this system will not work for the seed crisis.

Phnom Penh's poorly maintained runway could not stand the shock of repeated landings, critics say. Even if 10,000 tons were successfully delivered, this argument holds, they would pile up at the airport because Heng Samrin's chaotic fleets of trucks and river barges could not distribute them to village in time.

One alternative is a program begun last week to distribute seed at the Thai border. For months tens of thousands of people, most of them from western provinces which Heng Samrin's relief supplies have been slow in reaching, having come to the border to pick up rice and take it home.

The idea is to add seed to this traffic, which for unclear reason's is tolerated by the Phnom Penh government.

In the first two days, 300 tons of seed in 11- and 22-round sacks were passed out. Current plans call for about 10,000 tons to be sent into Cambodian villages this way. Most of it will be financed by a U.S. government grant of $2 million.

Already some Western diplomats are suggesting to the program might be accelerated to distribute seed in 88-pound sacks, putting 22,000 tons or over two-thirds of total needs across the border within six weeks. Other analysts question, however, whether the oxcarts and bicylces could move this volume in so short a time.

Earlier this year, Western relief experts announced Cambodia would require 30,000 tons of foreign seed this year. The U.N.'s Food and Agriculture Organization (FAO) was charged with procuring it for delivery through Red Cross and UNICEF. Vietnam later pledged to provide 10,000 of that and has already delivered an unknown quantity, relief sources said.

However, the FAO has so far landed only 620 tons of the remaining 20,000 required, according to relief sources.

Bureaucratic wrangles within FAO and the Thai government have been blamed for these delays. The FAO man in charge of seeds, for instance, was called to Rome headquarters in February and was away from the job for almost a month.

Moreover, after two months the Thai government has still made no response to FAO's request for an export license for 15,000 tons of seed being purchased here.Thai law discourages foreign sales of seed on the grounds of safeguarding the country's own supplies.

Relief scources said the FAO first submitted an application on Jan. 21. But a Cabinet reshuffle, then a change of prime ministers, paralyzed decisionmaking within the Thai bureacracy. Aid officials now hope clearance will come through this week.

Thai seed is considered the most desirable because ecological conditions in Thailand and Cambodia are similar. However, the FAO has been criticized for not looking to other countries when it became clear that Thai supplies would be delayed.

The 620 tons the FAO did deliver were brought in the Philippines which allowing free export of seed. "They were intend for the country's small dry season rice crop planted at the beginning of the year. But the shipment arrived late. Agriculturists later said this was party to blame for the dry season crop's poor showing.

Cross-border distribution has also run behind schedule. Due to start Feb. 6, it was postponed at least four times due to unfinished packing of the seed, arequest from the Red Cross to check with headquarters before taking part, and fighting along the border.

However, legal loopholes make export clearance unnecessary. The Cambodians cross into Thailand to pick up the supplies; therefore the relief agencies need no permit because they are not formally exporting them. The Cambodians are, but they cannot be monitored.

Food experts caution that rice deliveries must continue full force while seed is being sent in, arguing that if people run out of rice, they will consume the seed.